[sdiy] Polyphonic voice allocation algorithm

Terry Shultz thx1138 at earthlink.net
Mon Jun 23 23:32:16 CEST 2014

Hi Folks,

The Microprocessor based Polyphonic keyboard was patented by E-Mu 
Systems in 1976 by Dave Rossum.
E-Mu licensed this to Oberheim Elec., Sequential Circuits, Shultz Sound 
Desigm. and perhaps a few others I can't remember now.

They successfully defended this patent against Allen Organs and so 
forth. The Pratt-Read keyboard that E-Mu specified was used by many 
others, Oberheim, Sequential Circuits, PPG, and so forth.

It was originally implemented on an 8080 processor, but migrated to a 
Z-80 at Patent filing time I believe.

This patent I believe has run out but it should be located in a google 

Hopefully this helps you as I need to look at my source code to give you 
an exact answer on exact algorithm function.

It has been many years since I looked at this software.

best regards,

Terry Shultz

On 6/23/2014 1:57 PM, rburnett at richieburnett.co.uk wrote:
> Hi guys and girls,
> Does anyone have a link or document that gives a good explanation for 
> a basic polyphonic voice allocation algorithm.  I'm not after anything 
> fancy, just the sort of process that goes on inside a basic 
> mono-timbral polysynth like Roland's Juno series.
> I know some basic terminology like "voice stealing" and "round robin 
> fashion" but I'm trying to avoid sitting down and going through the 
> thought process of coming up with my own voice allocation algorithm 
> from scratch!  Life is too short to spend time re-inventing the wheel 
> when this algorithm has been used for decades and must surely be 
> documented somewhere?
> I know synths like the Juno 106 had two different poly voice 
> allocation modes on offer.  One of them assigns repetitive same notes 
> to new voices in round-robin fashion so that their release phases can 
> overlap, and the other mode plays the repeating same notes by just 
> retriggering the same module.  What I'm really looking for is 
> something like a flowchart, or text description of how the voice 
> allocation decisions are performed.
> I appreciate that things can get complicated when notes can arrive 
> from local keyboard vs over MIDI, and things like Sustain messages, 
> and multi-timbral setups are considered.  However, I'd like to keep it 
> simple at the moment so that I can just play about with some synthesis 
> options.
> Thanks in advance for any help,
> -Richie,
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